Recovery of cyclohexane and methyl



R. A. VAN NORDSTRAND ET AL 2,759,917 RECOVERY OF CYCLOHEXANE AND METHYL CYCLOPENTANE FROM PETROLEUM 2 Sheets-Sheet 2 Aug. 21, 1956 Filed Nov. 25, 1951 ATTORNEYS United States Patent RECOVERY OF CYCLOHEXANE'AND METHYL CYCLOPENTANE FROM PETROLEUM Robert A. Van Nordstrand, lossmoor, Ill., Harry Louis Pelzer, Ogden Dunes, Ind., and John W. Teter, Chicago, 11]., assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application November 23, 1951, Serial No. 257,676

2 Claims. (Cl. 260-965) Our invention relates to improvements in benzene production from C6 petroleum fractions. More particularly, it relates to a process for recovering cyclohexane and methyl cyclopentane from close-boiling Cs petroleum fractions in a form useful for benzene manufacture.

Most of the straight-run naphthas and casinghead gasolines contain an appreciable amount of cyclohexane in the C64 cut, i. e. the hydrocarbon fraction boiling in the range of about 130 to 230 F., and this hydrocarbon fraction thus represents a valuable potential source of cyclohexane for reforming into benzene. The Ca cuts also generally contain appreciable quantities of methyl cyclopentane which can be readily isomerized to cyclohexane either separately or in conjunction with the cyclohexane reforming operation. However, a representative Cs out which has been fractionated to obtain the highest practical concentration of cyclohexane may contain only about 40% cyclohexane and about 30% methyl cyclopentane. It is thus evident that the relatively high proportions of hydrocarbons other than methyl cyclopentane and cyclohexane in these Ce fractions decrease the yield of benzene which can be obtained by isomerization and reforming processes. Moreover, if it is desired to isomerize the methyl cyclopentane in an operation separate from the cyclohexane reforming operation, or if it is desired to separate the methyl cyclopentane for other applications, many difficulties are encountered in spite of a 16 F. boiling point difference between methyl cyclopentane and cyclohexane due to the multitude of azeotropes which are possible.

We have now found that cyclohexane and methyl cyclopentane may be recovered in substantially pure form from a petroleum hydrocarbon fraction boiling within the range of about 130 to 230 F. by treatment of such a hydrocarbon fraction with thiourea. For example, we have found that the boiling points of cyclohexane and methyl cyclopentane when in admixture with normal paraffins, isoparaflins, aromatics, other naphthenes, etc. are in effect elevated by intimately contacting the admixture with finely powdered thiourea in the presence of a small amount of water at a temperature of about 40 to 60 F. to form solid adducts of thiourea and cyclohexane and of thiourea and methyl cyclopentane in such a manner that the solid adduct forming hydrocarbons may be separated from the non-adduct forming hydrocarbons by stepwise distillation. The proportion of thiourea to cyclohexane and to methyl cyclopentane necessary to form the solid adduct is about three to one in each case but advantageously an excess of thiourea is employed. The hydrocarbons remaining in the liquid phase are distilled overhead at normal distillation temperatures, the solid adducts of cyclohexane and methyl cyclopentane are decomposed by raising the temperature about 20 F., and the cyclohexane and methyl cyclopentane are distilled over leaving the thiourea as bottoms in the still. The cyclohexane-methyl cyclopentane mixture may then be passed directly to a conventional reforming type unit for dehydro-isomerizing the methyl 'ice cyclopentane and dehydrogenating the cyclohexane to benzene in a concurrent operation, or the cyclohexanemethyl cyclopentane mixture may be conventionally fractionated and separately passed to reforming type units.

If the cyclohexane and methyl cyclopentane recovered by the process according to our invention are to be utilized in the manufacture of benzene, advantageously the C6 cut treated with thiourea should be a hydrocarbon fraction boiling in the range of about to F.

The amount of water present during the reaction period should be sufiicient to provide a concentrated solution on the surface of the thiourea, enabling the reaction to occur, but advantageously such that no observable liquid phase is created. With this concentration of water the entire mass of the adduct and thiourea remains solid throughout the distillation operation. Besides serving as a promoter of the urea-hydrocarbon adduct formation, the water serves an additional purpose during the stepwise distillation in that it provides sufficient vapor pressure to allow the hydrocarbons in the adduct to distill over at a somewhat reduced pressure and temperature, thereby aiding in the prevention of thiourea thermal decomposition.

The operation of our invention will be further described with reference to Figure I which represents a flow diagram of our novel process.

of line 14. The non-adduct forming hydrocarbons may be stripped from the slurry at temperatures below the normal boiling points of these hydrocarbons in distillation stage 13 by vacuum distillation or by stripping with warm air and withdrawn by means of line 15. The thiourea-hydrocarbon adduct may be decomposed in the same distillation stage or it may be passed to a separate distillation stage 16 by means of line 17. The temperature in distillation stage 16 is maintained about 20 F. higher than that in distillation stage 13 in order to decompose the thiourea-hydrocarbon adduct and the adduct forming hydrocarbons are withdrawn through line 18. Thiourea is withdrawn through line 19. The efliu ent from distillation stage 16 and line 18 may be passed directly by means of valve 20 and line 21 to a conventional dehydrogenation-isomerization stage 22 in which the methyl cyclopentane is dehydro-isomerized and the cyclohexane is dehydrogenated to form benzene, or the eflluent may be passed by means of valve 23 and line 24- to a conventional fractionation stage 25. Cyclohexane is withdrawn through line 26 and passed by means of valve 27 and line 28 to dehydrogenation stage 29. Methyl cyclopentane is withdrawn through line 30 and may be passed to storage by means of valved line 31 or passed to isomerization stage 32 by means of line 33. The isomerized methyl cyclopentane is withdrawn through line 34 and passed to dehydrogenation stage 29 by means of valve 35 and line 28.

The most useful catalyst for these reforming type operations are platinum on alumina catalysts which may be produced by adding the precious metal, usually as a sulfied sol or as chlorplatinic acid, to an alumina hydrogel. The alumina usually is promoted by incorporation of a fluoride or chloride. An alumina-silica base may be employed but advantageously it is presintered to reduce cracking activity. Other catalysts, however, may

a be used such as molybdena on alumina, molybdena on alumina-silica and chromia on alumina.

The usual dehydrogenation and isomerization conditions are employed. For example, a reaction temperature of within the range of about 800 to 950 F. is utilized at a pressure of about 50 to 1000 p. s. i. g. The ratio of hydrogen to hydrocarbon feed is within the range of about 2:1 to :1, and the liquid hourly space velocity is varied from about 0.5 to 8. In general, greater severity is required for optimum yield in the case of isomerization of the methyl cyclopentane. For this reason I prefer to fractionate the cyclohexane-methyl cyclopentane mixture, separately isomerize the methyl cyclopentane to cyclohexane, admix this isomerized methyl cyclopentane with the cyclohexane fraction, and dehydrogenate both fractions in a reforming type unit.

The recovery of cyclohexane and methyl cyclopentane from a C6 out according to my invention is illustrated in the following example.

Concentrations of various hydrocarbons were chosen as being very similar to theoretical concentrations taken from the bottom of the number two distillation column in a series of four columns necessary for C6 fractionation. The concentrations chosen were:

Milliliters Percent Component 33. 4 33 Cyclohexane.

25. 2 25 n-Hexane.

23. 2 24 Methyl cyclopentane.

10. 5 10. 5 2,4-dimethy1- pentane.

7. 1 7. 5 Benzene.

To this hydrocarbon mixture were added 200 grams of thiourea dampened with ml. of water with vigorous stirring and the precipitation was carried out at 50 F. A stepwise distillation was then performed. As shown in Figure 11, separation of cyclohexane from the original mixture yielded a volume of liquid representing approximately half of the original total volume containing:

Per cent Cyclohexane 68 Methyl cyclopentane 23 Benzene 5 n-Hexane 1 2,4-dimethylpentane 1 Impurities 2 Since methyl cyclopentane has a boiling point 10 C. lower than cyclohexane, these two remaining primary constituents could easily be separated by standard distillation procedures. The benzene concentration does not change appreciably, but is actually desirable where the cyclohexane is to be used in the manufacture of benzene.

We claim:

1. A process for recovering cyclohexane and methyl cyclopentane from petroleum hydrocarbons which comprises intimately contacting a petroleum hydrocarbon fraction boiling within the range of about -230 F. with finely divided powdered thiourea in the presence of a small amount of water for a period of time sufiicient to form a solid adduct, distilling the non-adduct forming hydrocarbons remaining in the liquid phase overhead at normal distillation temperatures, decomposing the solid adduct by raising the temperature about 20 F., distilling the adduct forming hydrocarbons from the decomposed solid adduct overhead, said adduct forming hydrocarbons including principally cyclohexane and methyl cyclopentane present in said fraction, and recovering said thiourea as bottoms.

2. The process of claim 1 in which the petroleum hydrocarbon fraction boils in the range of about to F.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,398 McMillan et al. Jan. 8, 1946 2,499,820 Fetterly Mar. 7, 1950 2,577,202 Lien et al Dec. 4, 1951 OTHER REFERENCES Redlich et al.: Jour. Amer. Chem. Soc., vol. 72 (Sept.

' 1950), pages 4161-2 (2 pages). 

1. A PROCESS FOR RECOVERING CYCLOHEXANE AND METHYL CYCLOPENTANE FROM PETROLEUM HYDROCARBONS WHICH COMPRISES INTIMATELY CONTACTING A PETROLEUM HYDROCARBON FRACTION BOILING WITHIN THE RANGE OF ABOUT 130*-230* F. WITH FINELY DIVIDED POWDERED THIOUREA IN THE PRESENCE OF A SMALL AMOUNT OF WATER FOR A PERIOD OF TIME SUFFICIENT TO FORM A SOLID ADDUCT, DISTILLING THE NON-ADDUCT FORMING HYDROCARBONS REMAINING IN THE LIQUID PHASE OVERHEAD AT NORMAL DISTILLATION TEMPERATURES, DECOMPOSING THE SOLID ADDUCT BY RAISING THE TEMPERATURE ABOUT 20* F., DISTILLING THE ADDUCT FORMING HYDROCARBONS FROM THE DECOMPOSED SOLID ADDUCT OVERHEAD, SAID ADDUCT FORMING HYDROCARBONS INCLUDING PRINCIPALLY CYCLOHEXANE AND 